[GeoffR]

I've been testing with the optimizeLegibility style on my Glo with firmware 3.19.5761 but I've also noticed these good and bad effects when using full justification:

Good:
* Ligatures work.
* The problem with lines containing em-dashes, ellipses, etc. not being properly justified is fixed.

Bad:
* Some words at the beginning of a line have extra-wide letter spacing.
* The spacing after the end of a sentence is sometimes much smaller than the spacing between words in the sentence.

Overall I think it is an improvement, but still not as good as in ePubs.

Edit: Also tested with -webkit-font-feature-settings: "liga", "dlig"; and all the effects are the same as with text-rendering: optimizeLegibility.

Edit: These screenshots show the differences on my Glo with the built-in Amasis font selected, reading a DRM KePub synced from Kobo. In the first screenshot, note the word "But" at the beginning of the second paragraph, and the justification of the last line on the page. In the second screenshot, note the spacing of the seventh line from the bottom reading "soon enough. Crusty, lichen-dotted carapaces":